Titanium primer for an evapor-ion pump



July 7, 1964 E. c. HURST 3,140,173 TITANIUM PRIMER FOR AN EVAPOR-ION PUMP Filed Dec. 27. 1962 INVENTOR. fidmazm 6'. flares? United States Patent 3,140,173 TITANIUM PRIMER FOR AN EVAPOR-ION PUMP Edmond C. Hurst, Stoughton, Wis, assignor to the United States of America as represented by the United States Atomic Energy Commission Filed Dec. '27, 1962, Ser. No. 247,775 4 Claims. (Cl. 75-200) This invention relates to evapor-ion pumps and more particularly to primers therefor.

The conventional primer of an evapor-ion pump comprises tungsten and titanium wires which are twisted together. The tungsten acts as a support for the titanium which is evaporated to provide a rapid initial gettering action for the evapor-ion pump. This type of primer is usable only once or twice before failure due to melting. The rate of evaporation of the titanium is not uniform along the length of the primer hence, hot spots develop in the tungsten wire causing it to melt and the primer to fail.

It is therefore one object of the present invention to provide a primer having a relatively uniform rate of evaporation throughout the length thereof.

It is another object of the present invention to provide a primer having a low susceptibility to hot spots.

It is another object of the present invention to provide a primer having a longer life than the conventional primer.

Other objects will become more apparent as the detailed description proceeds.

In general, the primer of the present invention comprises a porous tungsten cake formed around a titanium wire. The titanium is melted causing it to wet and diffuse through the tungsten cake.

Further understanding of the present invention may best be obtained from consideration of the accompanying drawing wherein is shown a coating of powdered tungsten and liquid binder formed around a titanium wire before heating.

A complete understanding of the structure of the primer may best be obtained from consideration of the method of construction thereof.

First, a mixture is made of powdered tungsten and a suitable binder. The binder may be of any material provided that it can be removed or evaporated from the mixture leaving a porous tungsten cake. Liquid Lucite having ethylene dichloride as a solvent has been found to be a suitable binder for the purposes of the present invention.

The mixture is then formed into a coating around a titanium wire 12 as shown in the accompanying drawing. The coating 10 is then allowed to cure until the ethylene dichloride solvent is evaporated from the Lucite binder. The wire 12 together with the coating 10 is placed in an evacuable chamber (not shown) and the chamber is evacuated to a pressure of at least 10' mm. of Hg.

Current is passed through the titanium wire 12 and is increased in value until the wire 12 is at a temperature of approximately 1500 C. or just below the melting point of titanium. The rate of increase of the current is governed by the rate of evaporation of the Lucite binder from the coating 10 and the ability of the vacuum pump to maintain the system at a pressure of at least 10 mm. of Hg.

The titanium wire 12 is held at this temperature for approximately one hour or until sufficient time has elapsed to eliminate as much of the Lucite as possible from the "ice coating 12 and form or sinter the powdered tungsten into a porous metallic cake around the titanium. wire 12. The current is then increased to a value at which the titanium wire 12 is caused to melt, whereupon it wets and diffuses through the tungsten cake. The current and partial vacuum is then removed and the primer is ready for use.

With the primer constructed in the aforementioned manner, a uniform rate of evaporation of titanium is obtained along the length thereof. This results in a substantial reduction in the susceptibilty of the primer to hot spots being developed therein with resulting burnout thereof. The thickness of the coating 10 on the titanium wire 12 is dependent upon the diameter of the titanium wire 12, that is, the more titanium to be stored in the primer, the thicker the coating 12 has to be. Further, the construction of the present primer permits the storage of more titanium therein than in the standard primer, thereby giving a longer usable life. Using inch diameter titanium wire, a tungsten-Lucite coating of approximate- 1y 7 inch radial thickness was placed thereon prior to sintering. After sintering the porous tungsten cake alone was approximately inch radial thickness and the resulting primer had an outside diameter of approximately inch. This primer was able to be reused at least 300 times versus once or twice for the standard primer.

Persons skilled in the art will, of course, readily adapt the teachings of the invention to embodiments far difierent than that illustrated. Accordingly, the scope of protection afforded the invention should not be limited to the particular embodiment shown in the drawing and described above but shall be determined only in accordance with the appended claims.

What is claimed is:

1. A method of manufacturing an evapor-ion pump primer comprising the steps of applying a mixture of powdered tungsten and a liquid binder to form a coating around a titanium wire, curing said coating until the solvent of said binder is evaporated therefrom, placing said coating and said wire in an evacuable chamber, evacuating said chamber, heating said wire to an initial temperature just under the melting point thereof, maintaining said wire at said temperature for a duration sufficient to remove said binder from said coating and form said tungsten into a porous tungsten cake, and raising the temperature of said wire until said Wire melts whereby the titanium wets and diffuses through said tungsten cake.

2. The method according to claim 1 wherein said evacuable chamber is evacuated to a pressure of at least 10- mm. of Hg.

3. The method according to claim 2 wherein the temperature of said titanium wire is raised to an initial temperature of approximately 1500 C. at a rate such that the vacuum of said evacuable chamber is maintained at a pressure of at least 10- mm. of Hg.

4. A method of manufacturing an evapor-ion pump primer comprising the steps of preparing a mixture of powdered tungsten and a liquid Lucite binder having ethylene dichloride solvent therein, applying said mixture to form a coating around a titanium wire, curing said coating until said ethylene dichloride is evaporated therefrom, placing said coating and said wire in an evacuable chamber, evacuating said chamber to a pressure of at least 10* mm. of Hg, applying current to said titanium Wire, increasing the value of said applied current until the temperature of said titanium wire is approximately 1500 C., maintaining said titanium wire at approximately 1500 3 4 C. for a duration sufiicient to remove said Lucite binder References Cited in the file of this patent from said coating and form said tungsten into a porous UNITED STATES PATENTS tungsten cake, increasing the value of said current to melt 2 699 008 Levi 16 1954 said titanium wire whereby it Wets and diffuses through 5 2:878:409 Levi Man 1959 s 'd tun sten cake, (1 'n 'd t d 'd 2.1 g an removl g sa1 curren an sa1 partial vacuum.

521,462 Canada Feb. 7, 1956 

1. A METHOD OF MANUFACTURING AN EVAPOR-ION PUMP PRIMER COMPRISING THE STEPS OF APPLYING A MIXTURE OF POWDERED TUNGSTEN AND A LIQUID BINDER TO FORM A COATING AROUND A TITANIUM WIRE, CURING SAID COATING UNTIL THE SOLVENT OF SAID BINDER IS EVAPORATED THEREFROM, PLACING SAID COATING AND SAID WIRE IN AN EVACUALBE CHAMBER, EVACUATING SAID CHAMBER, HEATING SAID WIRE TO AN INTITIAL TEMPERATURE JUST UNDER THE MELTING POINT THEREOF, MAINTAINING SAID WIRE AT SAID TEMPERATURE FOR A DURATION SUFFICIENT TO REMOVE SAID BINDER FROM SAID COATING AND FORM SAID TUNGSTEN INTO A PORTION TUNGSTEN CAKE, AND RAISING THE TEMPERATURE OF SAID WIRE UNTIL SAID WIRE MELTS WHEREBY THE TITANIUM WETS AND DIFFUSES THROUGH SAID TUNGSTEN CAKE. 